1. Field of the Invention
The present invention relates to a method for implementing a changeover between mixed light colors whose color loci can be specified in a color system, such as the CIE standard chromaticity diagram, by means of predetermining desired value sequences to a color control loop.
2. Discussion of the Prior Art
Such a method is known from DE 10 2004 047 669 A1 (in particular in connection with FIG. 6 therein). According to this document, light sources of the three primary colors red, green and blue, the three so-called primary valences, are energized independently of one another and their color emissions are additively mixed. Light sources such as lasers, electroluminescence elements, organic LEDs or in particular semiconductor light-emitting diodes are preferably used since their brightness is approximately linearly dependent on the duty ratio of the feeding with pulse-width-modulated constant current pulses. In the CIE standard chromaticity diagram depicted schematically therein, the resultant mixed light color locus is determined essentially by means of the instantaneous brightness contribution of each individual one of the three primary colors. This color locus can accordingly be displaced via at least one of the three brightness contributions and, as a result, each mixed light color can be set within a color triangle which is inscribed in the standard chromaticity diagram and whose corner points are given by the individual color emissions of the three light sources used for the illumination. The actually instantaneous contribution of the individual primary colors is measured by spectral colored light sensors as actual value transmitters of a controller. The controller alters the respective intensity of the emission by means of the duty ratio of the energization of the individual light sources in order to correct a possible instantaneous deviation from a predetermined mixed color, that is to say from the desired value of the color locus in the color triangle.
A mixed light color locus can thus be varied by variably predetermining the three primary color intensities as desired values to the controller. This change is manifested as a shift in the mixed-color light towards that one of the three primary colors whose brightness is increased in relation to the other two. The brightness is altered by way of the duty ratio of the energization of the respective colored light source. A continuous change in the duty ratio therefore brings about a change from an instantaneously given initial color locus to an intended target color locus in continuous transition through the various intervening color locus regions in the standard chromaticity diagram. Therefore, in the transition from one color locus to the next, mixed colors can occur whose visual impression is physiologically undesirable or even disturbing, especially if the color locus change extends over relatively long time spans. By way of example, in the background lighting of a theatre scene or in the lighting program for an aircraft passenger cabin it would be extremely unpleasant if, in the transition from dark-blue night light to red-dominant morning light, crimson color locus regions were also traversed, since the latter do not occur at all in the sunlight spectrum but lie in the direct mixture transition from the blue to the red colors. Less disturbing, by contrast, would be an intensity driving sequence such that a mixed color transition between blue B and red R takes place across the yellow Y color locus region. Switching off the previous color emission and switching on the future emission would be perceived as even more disturbing for lack of a gradual transition. On the other hand, for reasons of complexity it would be unrealistic to define, with respect to every actually conceivable pairing of initial and target color loci, the driving relations for all color mixtures which are possible during a gradual transition, which, under certain ambient conditions, are intended indeed not to appear, in order to be able for instance to mask out these color locus regions prior to their occurrence and to replace them by other color mixtures.